1. Field of the Invention
The present invention relates to distribution of a clock signal, and more particularly to a method and an apparatus for distributing a clock signal using standing waves.
2. Description of the Related Art
It is an important subject to synchronize operations and/or data transmissions in a digital system. In general, synchronization can be achieved and maintained by a clock signal. The clock signal may be supplied at unsynchronized time to circuits located at different positions. Such a time discrepancy of the clock signal is referred to as a “skew”. The skew has a bad effect on a digital system in the point of performance especially when the digital system operates at high speed. Therefore it is important that the clock signal is distributed uniformly to a whole system.
According to conventional methods, a clock distribution matrix is typically used for distributing a clock signal. In addition methods using standing waves have been proposed for distributing a clock signal to a whole system. An example of the methods is disclosed in U.S. Pat. No. 5,517,532 “Standing sine wave clock bus for clock distribution systems”. These conventional methods, however, can supply a clock signal only at limited positions.
U.S. Pat. No. 6,057,724 discloses a method such that, after generating a resonance signal in whole resonance plates having two resonance plates arranged in parallel, a clock signal is supplied without phase difference by extracting the clock signal from the upper resonance plate.
However, the U.S. Pat. No. 6,057,724 has a problem that only a fixed signal can be supplied since the resonance frequency of the resonance plates is fixed. Moreover, applying the method is strictly limited since a size of the resonance plates and a wave length of the clock signal are closely related. A wave length of the resonance signal is twice of the length of the resonance plate, and speed of light in a silicon semi-conductor is approximately a half of the speed in vacuum. For example, according to the U.S. Pat. No. 6,057,724, a silicon chip having a resonance plate, the length and width of which are 3.75 cm (centimeter), can supply only a clock signal of 2 GHz. There is a tendency that clock frequency is increased, but there is another tendency that size of chips is decreased and the clocks of various frequencies are needed according to operational mode. Therefore a clock distribution method capable of controlling the frequency of clock regardless of size of a resonance plate is required.